The present invention relates to a golf ball made of a core and a cover of one or more layer encasing the core. More particularly, the invention relates to an improved golf ball in which the microhardness of the cover is varied in the cross-sectional direction thereof, thereby endowing the ball with an excellent scuff resistance and spin properties and also an excellent feel on approach shots.
The outermost layer of the cover has hitherto been obtained by injection molding a specific resin material. Efforts have been made to lower the spin rate of the ball, improve the spin performance on approach shots, and also improve ball properties such as durability and scuff resistance, by suitably adjusting the material hardness of this outermost layer.
When commonly available general-purpose urethane materials for injection-molding are used as the cover material for golf balls, ball properties such as scuff resistance are inferior, and so various improvements have been carried out to date. For example, JP-A 2002-336378 describes a golf ball which uses a cover material made of a thermoplastic polyurethane material and an isocyanate mixture. JP 5212599 discloses a golf ball which has a high rebound and an excellent spin performance and scuff resistance, and the cover material for which has a high flowability, resulting in a high productivity.
However, although these golf balls do have an improved scuff resistance, given the harsh service environment of golf balls, an even higher level of scuff resistance has been desired. Also, common, general-purpose urethanes are inferior in terms of productivity and cost, in addition to which the foregoing conventional golf balls can hardly be said to have a good feel on approach shots.